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Gmelinite
0}, {10 1} and {0001} dominant. May also be tabular or rhombohedral. Crystals are striated parallel to (0001) | system = Hexagonal 6/m 2/m 2/m Dihexagonal Dipyramidal | lattice = a=13.78, c=10.03, Z=4 | twinning = Interpenetrant twins commonRoberts, Campbell and Rapp (1990) Encyclopedia of Minerals, 2nd edition on {10 1}. The twins consist of four individuals, three are at 90° to the other and at 60° to each other | cleavage = Good on {10 0} | fracture = Conchoidal | tenacity = Brittle | mohs = 4½ | luster = Dull to vitreous | refractive = nω = 1.476 - 1.494, nε = 1.474 - 1.480 | opticalprop = Uniaxial (-) | birefringence = δ = 0.002 - 0.014 | pleochroism = | streak = White | gravity = 2.04 to 2.17 | density = | melt = | fusibility = | diagnostic = | solubility = Soluble in cold 10% HCl. | diaphaneity = Transparent, translucent or opaque | other = Piezoelectric. Barely detectable radioactivity. As with all zeolites, water is released on heating, and almost all has been expelled by 400 °C. | references = http://www.webmineral.com/data/Gmelinite-Na.shtmlhttp://www.mindat.org/min-6973.html Mindat.org }} Gmelinite-Na is one of the rarer zeolites but the commonest member of the gmelinite series, gmelinite-Ca, gmelinite-K and gmelinite-Na. It is closely related to the very similar mineral chabazite. Gmelinite was named as a single species in 1825 after Christian Gottlob Gmelin (1792–1860) professor of chemistry and mineralogist from Tübingen, Germany, and in 1997 it was raised to the status of a series.Deer, Howie and Zussman (2004) Rock-Forming Minerals Volume 4B:690-696 Gmelinite-Na has been synthesised from Na-bearing aluminosilicate gels. The naturally occurring mineral forms striking crystals, shallow, six sided double pyramids, which can be colorless, white, pale yellow, greenish, orange, pink, and red. They have been compared to an angular flying saucer. Structure The aluminosilicate framework is composed of tetrahedra linked to form parallel double six-membered rings stacked in two different positions (A and B) in the repeating arrangement AABBAABB. The framework has no Al-Si order. Within the structure there are cavities with a cross-section of up to 4 Å, and also wide channels parallel to the c axis with a diameter of 6.4 Å.Senderov and Shishakova (1967) Russian Chemical Bulletin 16-1:151 Space group: P63/mmc. Unit cell parameters: a=13.72 Å, c=9.95 Å, Z=4. Environment Generally occurs in Si-poor volcanic rocks, marine basalts and breccias, associated with other sodium zeolites such as analcime, Na(Si2Al)O6·H2O, natrolite, Na2(Si3Al2)O10·2H2O, and chabazite-Na, Na2Ca(Si8Al4)O24·12H2O. It also occurs in Na-rich pegmatites in alkaline rocks, and as an alteration product in some nepheline syenite intrusions. No sedimentary gmelinite has been found.Gaines et al (1997) Dana's New Mineralogy Eighth Edition It is generally assumed that it forms at low temperatures, less than 100 °C. It is widespread as a hydrothermal alteration product of ussingite, Na2AlSi3O8(OH), associated with gobbinsite, Na5(Si11Al5)O32·11H2O, gonnardite, (Na,Ca)2(Si,Al)5O10·3H2O, and chabazite-K. Notable localities Gmelinite-Na occurs extremely rarely at the Francon Quarry, Montreal, Canada, in sills of the igneous volcanic rock phonolite which are rich in dawsonite, NaAl(CO3)(OH)2. Tarassoff, Peter, and Horvath, Lazlo and Elsa (2006) Mineralogical Record 37-1:35 It occurs both as pure gmelinite-Na and interlayered with chabazite in water-quenched basalts in Western Tasmania. Sutherland, F L and Bottrill, R S (2004) Zeolites of Western Tasmania, Australian Journal of Mineralogy 10-2: 59 - 72 Associated minerals include other zeolites, especially chabazite, quartz, aragonite and calcite. Distribution Type Locality: Monte Nero, San Pietro, Montecchio Maggiore, Vicenza Province, Veneto, Italy. Also found in Australia, Canada, Czech Republic, Germany, Hungary, Japan, Russia, UK and USA. References External links *Mineral galleries *Mindat Category:Sodium minerals Category:Calcium minerals Category:Aluminium minerals Category:Zeolites Category:Hexagonal minerals lb:Gmelinit nl:Gmeliniet pl:Gmelinit uk:Гмелініт